Classes and instances for Regex matching.
All the classes are declared here, and some common type aliases, and the MatchResult data type.
The only instances here are for Extract String and Extract ByteString. There are no data values. The RegexContext instances are in Text.Regex.Base.Context, except for ones which run afoul of a repeated variable (RegexContext regex a a), which are defined in each modules' String and ByteString modules.